1. Technical Field of the Invention
The present invention relates to a pulley unit including a one-way clutch.
2. Description of Related Art
Various accessories mounted on a vehicle engine are attached to a belt driven by an engine""s crankshaft. However, when an accessory such as an alternator is connected to the crankshaft of the engine, and rotated synchronistically with the crankshaft, the following problem occurs. That is, when a rotational speed of the crankshaft is reduced, alternator power generation is also reduced. Conventionally, to avoid such a problem, a pulley unit containing a one-way clutch is used for a vehicle alternator so as to improve power generation efficiency when the rotational speed of the crankshaft is reduced.
FIG. 8 is a related art, cross-sectional view showing a conventional pulley unit containing a one-way clutch. As shown in FIG. 8, the conventional pulley unit includes a pulley 200, a shaft body 210 and a one-way clutch 220. The pulley 200 and the shaft body 210 are concentrically disposed, and the one-way clutch 220 is disposed in a space therebetween at a middle position in an axial direction. The one-way clutch 220 is composed of an outer ring 222 fixed to the pulley 200, an inner ring 224 fixed to the shaft body 210, and plural cylindrical rollers 226 sandwiched between the outer ring 222 and the inner ring 224. The outer ring 222 and the inner ring 224 define a plurality of wedge-shaped spaces therebetween in a circumferential direction. The rollers 226 are disposed in these wedge-shaped spaces, thereby constructing the one-way clutch 220 for transmitting rotational driving force only in a single direction.
The one-way clutch 220 is switched using this type pulley unit between a locked condition (driving-force transmitting condition) and a free condition (driving-force interrupting condition) in accordance with a revolution speed difference between a rotor of the vehicle alternator, integrated to the shaft body 210, and the pulley 200. Thus, a driving force can be transmitted and interrupted between the rotor and the pulley 200. Two bearings 230 are provided at both ends of the one-way clutch 220 in its axial direction, respectively, so as to smooth any relative rotational operation between the rotor and the pulley 200 and to undertake a load added from the belt.
In the above conventional pulley unit, the shaft body 210, provided inside the one-way clutch 220 in its radial direction, defines an attachment through hole at its center. The pulley unit is attached to a shaft of an accessory using this attachment through hole. Therefore, when water hits an end surface of the pulley unit used in a state where the pulley unit is attached to the crankshaft, the water enters between the shaft body 210 and the shaft. Then, portions covered with the water rust, and it is difficult to remove the pulley unit from the shaft. Water, hitting the end surface of the pulley unit, is generally prevented from entering the pulley unit by a cap covering the end surface of the pulley unit. However, because of this arrangement, the number of components must be increased making an attachment process complicated, thereby increasing production costs.
It has been considered that a diameter of a pulley unit be reduced to increase a rotational speed of the accessory. The conventional pulley unit shown in FIG. 8 defines the attachment through hole at its center, and the one-way clutch 220 is provided outside the attachment through hole. Therefore, the conventional pulley unit has a complicated structure in its radial direction, and the diameter of the pulley unit is difficult to reduce.
There are screw portions, each provided on the shaft and a surface defining the attachment through hole, inside the one-way clutch 220 in its radial direction. When the pulley unit is attached to the shaft, the screw portions are clamped to each other so that the shaft body 210 is deformed outside in its radial direction by a clamping force in its axial direction by force received from the screw portions. Therefore, the shape of the plural wedge-shaped spaces, provided in the one-way clutch 220 in its circumferential direction, where the plurality of rollers 226 are contained, changes. As a result, the one-way clutch 220 sometimes does not operate in a normal, stable fashion.
FIG. 3 is a related art, cross-sectional view that exemplifies a case where the cam surface 224a is deformed in the radial direction in a conventional pulley unit. As shown, the wedge angle of the wedge-shaped space, formed between the outer ring 222 and the inner ring 224, controls the position of roller 226 and changes the wedge-shaped space from a wedge angle xcex81, at which the cam surface is not deformed, to a wedge angle xcex82, at which the cam surface is deformed. Therefore, the rotational speed at which either the lock or free state switches, varies in accordance with the degree of deformation, thereby degrading operational stability.
The present invention has been made in view of the above problems, and an object is to provide a pulley unit with a diameter that can be reduced, whose operation can be stabilized, and that is readily removable after being used, without increasing current production costs.
In order to solve the above problems, a pulley unit of the present invention includes a one-way clutch disposed between a pulley and a shaft body which are arranged concentrically. In the pulley unit, further, the one-way clutch includes a roller contained in a wedge-shaped space. The shaft body includes a shaft attachment portion, by which the shaft body is integrated to the shaft, at a position which is not overlapped with the roller in an axial direction. Since the shaft attachment portion is not provided inside the roller in a radial direction, a radial cross-sectional structure of the pulley unit can be simplified at this portion, and a diameter thereof can be reduced.
Preferably, the shaft attachment portion is a female screw portion clamped to a male screw portion provided on an outer surface of the shaft. Generally, the pulley unit is required to be clamped or fixed to the male screw portion of the shaft by a large force so as to prevent falling and circular movement of the pulley unit. In the pulley unit, since the female screw portion is not formed inside the roller in a radial direction, a wedge-shaped space around the roller is not deformed by a clamping force generated in an axial direction at a clamping time by force received from the male screw portion of the shaft, thereby stabilizing operation of the one-way clutch.
The above shaft attachment portion, having a recessed shape, is provided on an end surface of the shaft body, and preferably, the shaft body is formed in a non-through structure, that is, the shaft body defines a non-through hole. Therefore, when water strikes the end surface of the pulley unit, it is prevented from entering the clamped portion between the shaft and the shaft body, thereby preventing rust from forming. Accordingly, the pulley unit can be readily removed from the vehicle after being used without increasing production cost, and using a cap and the like.
Preferably, the above shaft body includes a projection-shaped screwing portion, by which the shaft body is clamped to the shaft, on an end surface at an opposite side of the shaft attachment portion. Since the screwing portion is not required to be provided inside the shaft body, a diameter of the shaft body can be reduced by a diameter of the screwing portion, thereby further reducing a diameter of the pulley unit.
Preferably, the above shaft body is formed by fixing, to each other, a member where the one-way clutch is formed facing the roller, and a separate member having the shaft attachment portion. When the shaft attachment portion is a separate member, heat treatment for improving abrasion resistance is permitted only for the member where the one-way clutch is formed. Therefore, production equipment costs can be reduced while heat treatment time is shortened, thereby reducing production costs.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.